I have noticed that my colleague Martin have already answered to the other support ticket that you have opened on the same topic.
I was able to reproduce the issue locally and confirm that the grid does not behave as expected in this scenario. I have forwarded your report to our developers for further investigation. Unfortunately, I can not provide you with exact estimate about when the problem will be fixed. However, you can follow the status of the issue in our public issue tracking system (you may need to log in to view the issue details under "Your Tracked Issues" section).
To avoid duplicate posts I would suggest that you continue your communication there.
All the best,
the Telerik team